IPhone – Will I lose the messages if I downgrade the iPhone from iOS 5 to iOS 4

Ok, so after some quick googling and reading some Apple forums, it looks like iCloud (in iOS 5.x) isn't ready for prime time. I've done the following and now iOS 5.x seems a lot snappier.

1. Disabled iCloud everywhere (Settings -> iCloud)

   Disable all apps then Scroll down and hit "Storage and Backup" and disable iCloud backups. If you really want to go strong, just delete your iCloud account setting (on your phone, Settings -> iCloud -> scroll to bottom)

2. Disabled sending data to Apple (Settings -> General -> About -> Diagnostic & Usage -> "Don't send")

3. Minimized Location Services (Settings -> Location services)

   I kept it ON globally, but disabled it for certain Apps Most importantly, disabled it for "Diagnostic & Usage" as well as "Location based iAds" (Settings -> Location services -> Scroll to bottom -> System Services)

4. Disabled notifications for the calendar (Settings -> Notification)

   I also removed notifications for many other apps that had added themselves ... However, I suspect this is fixed in iOS 5.0.1 under their "Battery issue fixed" patch. Earlier, Calendar notifications would hang causing CPU to be stuck 100%, draining the battery and leaving little CPU for other items.

Also, there are two apps, SysStatsMon and System Status. Both are good tools to see CPU usage on your iOS device. About 5+ seconds after launching them under normal circumstances, your CPU should be in the 5-15% range.

I'm surprised that you found an SHSH blob for a firmware that low. Consider that a treasure. Unfortunately, though, you can only install the version of iOS that corresponds to the SHSH blob. The blob contains a signature that is unique to the device and unique to the iOS version. It is like the key to your device for that version. It can't be faked, but it can be saved. So in short, you're stuck with iOS 4.1 or 5.1.1, and there isn't anything that can be done now to change that (besides, the change from iOS 4.1 to 4.3 only added AirPlay/Print, Safari's Nitro JavaScript engine, iTunes Sharing, and Ping; which shouldn't be big enough features to worry about unless your app integrates AirPlay).